I want the merge in the feature branch because I want to ensure we're
using the same mechanism for custom code etc

There are now three targets for documentation:
`doc_doxygen` --- this runs doxygen on the CPP source code
`doc_html`    --- this runs sphinx on the python code, and it uses the
                  available doxygen xml output to generate
                  sphinx_html/...
`doc_latex`   --- this runs sphinx on the python code, and it uses the
                  available doxygen xml output to generate
                  sphinx_latex/...
I can't get it to a point where I can run just "make doc_latex", I need
separate runs of pdflatex, but I guess that's negligible.

Latex wasn't working because the README contains a link to an image that
cannot be converted. So I asked that the image only appears in html.
There were also some strange problems with the markdown math syntax, so
I switched to full LaTeX which seems to be working.

used to collect pairs of different processes via standard MPI
communications, later to be optimized.

only looks for existing source files now.

 Conflicts:
        cpp/full_code/static_field_with_ghost_collisions.cpp
        cpp/full_code/static_field_with_ghost_collisions.hpp

 Not sure why conflicts exist

code does not work for more than one thread per MPI process.